The thoracic (T) spine contains 12 vertebrae, also referred to as dorsal vertebrae of the spine. The vertebral bodies decrease in size from T1 to T3 and then successively increase in their morphometric parameters through T12. Morphologically, the thoracic vertebrae are distinct from cervical and lumbar subtypes in that they have rib articulations, heart-shaped vertebral bodies, unique facet orientations, and elongated spinous processes. At the transitional zones, however, the thoracic vertebrae may share morphologic features with distal cervical or proximal lumbar vertebrae.

The vertebral bodies of the thoracic spine are typically smaller and narrower as compared to lumbar counterparts. In some instances the heart-shaped posterior aspect of the vertebral body may extend lateral to the pedicles in the axial plane. The projection of the vertebral bodies in relation to the posterior elements, along with the morphometric parameters of the intervertebral disks in the thoracic region contributes to the anatomically normal thoracic kyphosis which is generally described as lying within the range of 20 to 40 degrees. Thoracic kyphosis that exceeds 45 degrees, or is less than 20 degrees, is considered outside the normal range.

Thoracic transverse processes are angled posteriorly due to the rib articulation and intersect with the pars interarticularis. Thoracic laminae are shallow and flow into the larger spinous processes which overlap the caudal vertebrae creating a shingling effect within the dorsal spine. Pedicles are angled anteromedially from their origin just distal to the superior articular facet. Medial angulation of the pedicles decreases successively, however, within each distal vertebral segment of the thoracic spine. Proximal thoracic pedicles can be exceptionally narrow, especially in the setting of spinal deformity or congenitally anomalous vertebrae. Classically, the T4 pedicle is thought to be the narrowest pedicle within the thoracic spine.

The superior and inferior articular processes of adjacent vertebrae articulate to form thoracic facet joints. The facet articulation of the superior articular process faces dorsally, while the articulation of the inferior process is oriented ventrally. In the proximal and midthoracic region, the facets are coronally oriented. The facet joints become progressively more sagittally oriented in the more distal regions of the thoracic spine.

A unique aspect of the thoracic spine is the rib articulations, which are present bilaterally. The rib cage creates a so-called “fourth column” within the thoracic spine, adding stability and limiting the capacity for flexion, extension, and rotation between thoracic segments. The ribs typically articulate with the thoracic vertebrae at two locations (Fig. 28.1):

The rib articulates with its named vertebral body just inferior to the intervertebral disk space. Thus, the eighth rib connects to T8 at its superior costal facet and transverse process. Following the course of the eighth rib along its superior border will allow access to the T7–T8 disk space.

The first through seventh ribs are termed “true” ribs and articulate with the sternum. Ribs 8, 9, and 10 are called “false” due to their connections with the costal cartilage. Ribs 11 and 12 are deemed “floating” and have no anterior articulations. Nor do these ribs articulate with the transverse processes of their named vertebrae.

The spinal cord runs throughout the thoracic spine and transmits nerve roots beneath the pedicles of the named vertebrae. For example, the T10 nerve roots exit beneath the pedicle of the T10 vertebra. The T1 nerves supply sensation of the ulnar forearm and T2 supplies the axilla. T1 motor innervation is associated with interosseous muscle function in the hands. Successive thoracic dermatomes supply the trunk with the T4 dermatome associated with the region of the nipples, T7 at the
inferior aspect of the sternum, and T10 at the level of the umbilicus. The superficial abdominal reflex is controlled by the distal thoracic nerve roots from T7 to T12.

The blood supply to the thoracic vertebrae, intervertebral disks, and the spinal cord derives from medullary vessels that arise from the descending aorta and communicate with the spinal arteries through the intervertebral foramen, where the medullary arteries travel with the thoracic nerve roots. The anterior spinal artery and the two posterior spinal arteries may exist as single contiguous entities or a number of segmented vessels with extensive arborizations of collateral vessels. Significant medullary vessels are thought to exist at the T3, T8, and T10–T11 regions, creating “watershed” zones within the thoracic spinal cord. Only certain radiculomedullary vessels become contiguous with the anterior spinal artery, whereas most terminate in the pial plexus or plexi around the nerve roots. The juncture between the anterior artery and the radicular vessels can be tenuous as the vessel loop makes a “hairpin” turn at the vascular confluence. The largest of these radiculomedullary arteries, the arteria medullaris magna or artery of Adamkiewicz, usually enters the spinal canal at the level of T10 or T11 (Fig. 28.2). Damage to this vessel, which is difficult to identify in all instances due to variable anatomy, can result in catastrophic neurologic deficit from ischemia.

The ligamentous structures responsible for stability of the thoracic spine are contiguous with counterparts in the cervical and lumbar regions. The anterior longitudinal ligament traverses the anterior aspect of the vertebral bodies and is anchored to the vertebral periosteum and the outer annulus of the intervertebral disk. Within the spinal canal, the posterior longitudinal ligament runs along the posterior vertebral bodies and intervertebral disks, while the ligamentum flavum anchors to adjacent laminae. The ligamentum flavum is not a continuous structure, but rather covers the interlaminar window at each vertebral level with a caudal origin near the superior aspect of the lamina and a cranial insertion point near the midventral lamina of the upper level. The interspinous and supraspinous ligaments connect the spinous processes.

Most of the major back muscles have articulations with the thoracic vertebrae. The most superficial layer consists of the trapezius and latissimus dorsi with the rhomboids and serratus posterior forming the middle layer (Fig. 28.3). The serratus posterior inferior originates

from the inferior aspect of the posterior ribs and inserts on the posterior elements of the inferior thoracic vertebrae at T10–T12 as well as the proximal lumbar vertebrae. The serratus posterior superior inserts on the proximal thoracic vertebrae. The erector spinae musculature (e.g., spinalis, longissimus, iliocostalis) has multiple insertions at nearly every level in the thoracic spine. The different muscle layers, individual muscles, and their insertion points on the thoracic spine are not typically visible during surgical dissection.

Anterior surgery of the thoracic spine can be used to address the following conditions:

Preoperative planning includes obtaining appropriate imaging of the intended levels and anticipating the scope of exposure needed, including rib resection and possible diaphragmatic take down. Given the risk for pulmonary complications, assessment of preoperative lung function in smokers or patients with chronic lung disease is prudent in identifying those for whom alternative approaches should be considered. Limitations of the surgery, such as the inability to access contralateral pedicles and the posterior elements should be understood. Collaboration with an experienced general surgeon can aid in safe and timely exposure.